Time for a new groomer. I know they get busy and might forget, but that is no excuse for something that takes so long to grow out. Don't forget to let them know why you will not be coming back.
I usually write out a 3x5 card to give the groomer if there is something I want them to remember. (I do this at the doctor for myself also) Jot down your phone number so they have it handy for a quick call without having to look up your file. And don't forget a nice tip--that works wonders!